1. Field of the Invention
This invention relates to the field of hollow fiber membrane type blood oxygenators. In particular, it relates to a unique design of hollow fiber membrane type oxygenators with a wound gas exchange membrane and a wound heat exchanger, which allows for a low prime volume, high gas transfer rate, high heat exchange efficiency and low pressure drop.
2. Description of the Related Art
From the first operation to repair a heart in 1891 until the early 1950s, heart surgeons were limited by the problem of trying to work on the heart while it was still beating. The heart's constant motion, and the presence of blood that obscured the surgeon's view, made repairing heart defects a surgical challenge. Surgeons had to work quickly and there was always a danger of disrupting blood circulation to vital organs. The solution to this problem came in the late 1950s with the development of the first oxygenators.
In nature, deoxygenated blood from the veins returns to the heart's right atrium. From the right atrium, blood is pumped to the right ventricle, then through the pulmonary artery to the lungs. The lung oxygenates the blood while removing carbon dioxide as it passes through the lung's alveolar capillary network. Oxygenated blood is then returned to the left atrium by way of the pulmonary veins. Blood is then pumped through the mitral valve into the left ventricle and pumped back into the body's circulatory system. Cells are replenished with oxygen and carbon dioxide is taken up by the blood as the blood passes through the body's capillary system. After this gaseous exchange is accomplished, the blood is returned to the heart and the cycle is repeated.
During cardiopulmonary surgery, venous blood is taken from the patient's circulation by means of a canula placed in the vena cavae. The blood "bypasses" the heart and lungs and enters what is referred to as the "extracorporeal circuit" or literally a circuit "outside the body." Oxygenation of the patient's blood takes place in an oxygenator much in the same way as it does in the natural process. After the blood is oxygenated and temperature regulated, it is returned to the patient's arterial circulation through a cannula so that the patient's body may utilize the oxygenated blood.
Ideally, therefore, oxygenators used in cardiopulmonary bypass surgery should emulate the natural process by ensuring that the blood is sufficiently oxygenated. In addition, an oxygenator must regulate the temperature of the blood and provide low pressure drops. Moreover, an oxygenator utilizing a low prime volume is desirable.